Answer:15
Step-by-step explanation:
Given
Craftsman sell 10 Jewelry set for $500 each
For each additional set he will decrease the price by $ 25
Suppose he sells n set over 10 set
Earning
Earning 

differentiate to get the maximum value

Equate
to get maximum value



Thus must sell 5 extra set to maximize its earnings.
Answer:
5.833
Step-by-step explanation:
SIX MINUS 0.617 IS 5.833
The original price of the ring is <span>£</span>1400